The present invention relates to a dot printing apparatus and a method for printing on a recording medium, using a plurality of printing elements.
Hitherto, as shown in FIG. 1, a printing head 1, in a dot printer equipped with a plurality of printing elements, is constituted such that a plurality of printing elements 2A are arranged in a line, in contact with one another in the sub-scanning (vertical) direction. Such a structure can be realized in some types of printer, such as a wire dot printer. However, in the printing head of an ink jet printer, the printing elements cannot be arranged in contact with one another, since a relatively large space needs to be provided around each printing element. Therefore, printing elements 2B are arranged in a zigzag form as shown in FIG. 2, or printing elements 2C are arranged on an oblique line as shown in FIG. 3.
In any of those types, as shown in FIG. 4, each time printing head 1 is driven in the main scanning (horizontal) direction to print one line of character data, the recording medium is moved upward in the sub-scanning direction by a distance equal to the dimension (in the sub-scanning direction) of the array of printing elements 2.
In the case where the space occupied by each printing element is large, as in an ink jet printer, the printing elements are arranged as shown in FIGS. 2 or 3; consequently, the width (the dimension in the main scanning direction) of printing head 1 increases. Due to the increase in the width of printing head 1, the distance of movement in the main scanning direction of this printing head 1 must be increased by a distance equal to twice the width in the main scanning direction of the array of the printing elements, so that the whole size of the printer is enlarged. This is the first problem.
With conventional types of printer, the dot pitch (the distance between the centers of two adjacent dots) in the sub-scanning direction cannot be made shorter than the interval of the printing elements. This is the second problem.
Further, as shown in FIG. 4, if the pitch in the sub-scanning direction of printing head 1 is set larger than the dimension (in the sub-scanning direction) of the whole length of printing elements 2, when the dots are printed by activating all of the printing elements, a white line will be produced in a boundary portion A of the adjacent main scanning regions. On the other hand, in the case where the pitch in the sub-scanning direction of printing head 1 is set smaller than the dimension (in the sub-scanning direction) of whole printing elements 2, a darker black line will be formed in the boundary portion. This is the third problem.